206 ELEMENTS OF BOTANY. 



stomata from becoming clogged with water, and the hairy net- 

 work on the under side of the leaf (into which they often 

 open) may sometimes serve to prevent them from becoming 

 clogged with dust, and certainly often hinders too rapid 

 transpiration. 



In regions where there is a long rainless season, many 

 plants produce bulbs in which their nourishment, acquired 



FiO. 185. —Arctic WiUow. The greater part of a pistillate plant, about 

 natural size. 



during the growing season, is buried until the next rainy 

 period comes round. 



Desert plants are commonly fleshy and often leafless, in 

 the latter case offering to the dry, scorching air only a small 

 surface of green bark through which transpiration and 



